Ensure dates are unique

When computing the quantity with delta, we must ensure that the start and end
dates are always different otherwise the delta quantity is always zero for
duplicated days (like today).

issue9942
review343181002

product.py

@@ -529,7 +529,7 @@ class ProductQuantitiesByWarehouse(ModelSQL, ModelView):
             key = trans_context['product_template']
         warehouse_id = trans_context.get('warehouse')
 
-        dates = sorted(l.date for l in lines)
+        dates = sorted({l.date for l in lines})
         quantities = {}
         date_start = None
         for date in dates:
@@ -538,6 +538,7 @@ class ProductQuantitiesByWarehouse(ModelSQL, ModelView):
                 'stock_date_end': date,
                 'forecast': True,
                 }
+            assert date != date_start
             with Transaction().set_context(**context):
                 quantities[date] = Product.products_by_location(
                     [warehouse_id],